Pressure-operated starting device



y 20, 1952 E. H. HULL ET AL 2,597,641

PRESSURE-OPERATED STARTING DEVICE Filed Dec. 5, 1945 Inventors: EdwinHull, Arthur F. Winslow,

is Attorney.

Patented May 20, 1952 UNITED STATES PATENT OFFICE PRESSURE-OPERATEDSTARTING DEVICE Edwin H. Hull, Schenectady, and Arthur F. Winslow,Scotia, N. Y., assignors to General Electric Company, a corporation ofNew York Application December 3, 1945, Serial No. 632,548

Claims. (Cl. 102-39) bustion of a powder charge is employed for startingfrom rest or powering devices, such as gyroscopes, single strokepistonand cylinder-devices, electric circuit breakers, and, in general,devices which are intended to be put into operation in a fraction of asecond or. are intended to be run for short periods. Such devices aresubject to damage if the burning of the charge occurs with too greatviolence.

In accordance with our present invention we have provided a novelcombination of large-sized, slow-burning powder pellets in combinationwith externally afiixed discrete, small grains of fasterburning powder.In accordance with a feature of our invention, we have provided acombustion device for burning such pellets in combination with means forrestraining movement thereof when ignited.

Apparatus embodying our invention is illustrated: by the accompanyingdrawing in which Fig. l is a vertical section of an ignition andcombustion device; Fig. 2 is an enlarged sectional view of thecombustion chamber showing a charge in operative position; and Figs. 3to 6 illustrate modified powder pellets.

The apparatus shown in Fig. 1 comprises a channel-shaped combustionchamber I which is connected by a conduit 2 to a device 3 which is to berapidly energized by gas under pressure. As such device may assumevarious forms, and itself is not a part of the present invention, it hasbeen merely indicated in the drawing. The conduit 2 terminates in aconical perforated diaphragm 4, herein termed a grate, providing spacesthrough which the gaseous combustion products enter the conduit 2. Abovethe grate is located a frangible diaphragm 5 which is ruptured ifexcessive pressure should be generated, thereby venting the excesspressure into a relief conduit 6. The diaphragm 5, which may consist ofsteel, or brass, or any non-brittle metal, is provided with a depressedring-shaped channel I which weakens the resistance to excessive internalpressure of the diaphragm. Exessive internal pressure will cause thediaphragm to bulge and finally to be ruptured at a region inwardlyspaced from the edge of the restraining wall of the conduit 6.

Into the combustion chamber communicatingwith the conduit 2 through theorifices of the grate is inserted a cartridge 8 which may consist of a12-gauge standard brass case having a crimped end 8 and containingpropellant pellets 9 of combustion material. The pellets 9 may consistof a single base" smokeless cannon powder and, in general, of acolloidal nitrocellulose, or may consist of a double base smokelesspowder, such as cordite, comprising mixtures of nitrocellulose andnitroglycerine. The pellets also may consist of nitrocellulose powders,either single or doube base, mixed with other ingredients such asoxidizers and metals. The pellets may consist of the so-called rocketpowders which are mixtures "of tars or rubbers with oxidizing agents,such as perchlorates of ammonium or potassium, and a plasticizer.

The pellets of propellant, smokeless powder burn at the rate of about .2inch per second per thousand pound pressure per square inch of surface,the rate of burningincreasing with the pressure at about the .9 power.If such pellets were packed in a cartridge in direct contact with anignition means, such as a primer, a too sudden burning of the pelletswith accompanying gasification might result in damage to the apparatus.

. Uncontrolled ignition is one of the major difficulties in usinglarge-grained smokeless powder.

The usual ignition method is to use a burst of flame from a charge ofblack powder or other ignition device. Uneven ignition of the powdergrains or pellets often results from such ignition due to the geometryof the grains, method of packing in the container, etc.

When the pellets are coated as described hereinafter, all of the pelletsare ignited on all surfaces in a short finite time in a repeatablemanner.

If the powder pellets were allowed to come into direct contact with theprimer, they might be split by the primer explosion. If the powderpellets were allowed any freedom of motion inside the cartridge orcombustion chamber, they might be blown against the grate and be split,resulting in too rapid combustion as well as damaging of the grate.

In accordance with a feature of our invention, the pellets 9 are urgedinto contact with the grate 4 by a spring I0 which is partly compressedagainst the end wall II when the cartridge is inserted, and urges thepellets against the crimped end 8 of the cartridge. A breech plug I2holds the cartridge in place and compresses the spring upon insertion ofthe cartridge, as shown in Fig.

1. In a perforation of the wall I I of the cartridge is inserted apercussion cap l3 (Fig. 2). A firing pin l4 explodes the cap when thefiring pin is struck at its exterior end.

In Fig. 1 is shown a magnetically released spring-operated hammermechanism l5 for striking the firing pin. A magnet l6 trips the latch 11when the energizing circuit i8 is closed, as by the operation of a pushbutton 25. The spring-operated latch II, when released, trips the hammer15 which is set under spring tension, as indicated. The hammer strikesthe firing pin 14 and causes it to detonate the percussion cap l3. Theblast of flame from the exploding cap l3 ignites the fuel pellets 9.

As shown in the drawing, pellets 9 are coated with small grains of afaster-burning, more easily ignited powder. The igniting grains adheringto the surface of the powder pellet, which are indicated in the drawingby stippling, are distributed over the surface of the pellet. The grainsmay consist of an easily ignitible substance such as conventionalpyro-technic ignitors. They may consist, for example, of ordinary blackpowder, modified black powder, of a mixture of an organic oxygen-bearingsubstance and a suitable quick-burning fuel, of a fibrous form ofnitrocellulose or semi-colloidal nitrocellulose commonly called blankfire, smokeless powder, or of a very finely divided colloidalnitrocellulose (smokeless powder). The .relatively massive, dense powderpellets 9 are. provided with a frosting of adhering grains of thefaster-burning powder. Adhesion of the grains to the powder pellets isinsured by coating the pellets with an ignitible adhesive, such ascellulose nitrate dissolved in a volatile solvent, as, for example,aeetone, or the large grains may be dipped in acetone to provide asticky surface. Upon partial evaporation of the solvent, the stillsticky pellets have the quick-burning powder grains applied in anysuitable manner. The exterior frosting of quick-burning powder startscombustion of the slower-burning, less-ignitible large pellets eventhough they are positioned at some distance from the igniter cap 13. Insome cases it is desirable to provide a single hollow combustion pelletof greater length, as shown in Fig. 3, in place of a plurality ofpellets, as shown in Fig. 2. The powder stick shown in Fig. 3 has alongitudinal aperture as indicated.

In other cases it is desirable that combustion of a massive powder grainshould be regulated so that combustion occurs at part of its surfaceonly. In Fig. 4 are shown in section two powder pellets 20, 2! placedend-to-end. The side surfaces are coated with a flame-excluding material22 which may consist of conventional friction tape. The end surfaces areuncoated. Grains 23 of fast-burning powder, such as above described, areaffixed upon the external surfaces of the ends of the pellets 20, 2| andupon the exterior'exposed surface of the tape. If the grains 23;areignited, as by a percussion cap, suchas shown in Fig. 2, they act as afuse to carry the ignition to the exposed end surfaces of the pellets20, 21 which are consumed endwise only, thereby slowing down theircombustion.

The pellet 24, Fig. 5, is coated with ignitionexcluding material, suchas a suitable tape, except for-one exposed end surface. Grains offastburning, easily ignitible powder are affixed upon the entireexterior surface but ignite the pellet only at its exposed end surface.In Fig.6 a pellet of powder is shown which is coated withignitionexcluding material except for an end surface which is the onlysurface coated with grains of fast-burning powder. This coated surfacewill become ignited by the cap 13 to which it is juxtaposed in acartridge, the remaining surfaces being shielded from ignition.

Regardless of the number or shape of the combustion pellets, they shouldbe held fixedly against the grate, as by a compressed spring 10. Aclosure pad 19 of nitrocellulose, or other suitable combustiblematerial, preferably is interposed between the grate and the combustiblepellet or pellets. In some cases the grate may be omitted, as when thecartridge is to be used for propelling a projectile (not shown).

In order to obtain the best efiiciency, it is desirable to have thecombustion chamber volume relatively small and to employ high pressuresof the order of 15,000 to 25,000 pounds per square inch. Three solidpellets of smokeless powder, such as shown in Fig. 2, about 0.672 to0.675 inch in diameter and having a total length of 1.9 to 2.2 inches,are desirable for use with a nozzle having a throat diameter of about0.05 inch. The combustion of the charge delivers gas at a pressurewithin the specified range over a period of about 0.2 to 0.3 second. Ifa somewhat lower pressure range of about 10,000 to 15,000 pounds persquare inch is desired, an elongated, apertured, cylindrical stick ofsmokeless powder is desirable. Such a stick, which is shown in Fig. 3,may have a diameter of about 0.672 to 0.675 inch and an aperture ofabout 0.082 inch.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A massive pellet of projectile-propellant powder, a flame-excludinglayer of material covering part of the surface of said pellet andclosely adjacent, discrete grains of fasterburning powder affixed tosurfaces of said pellet including the entire outer surface of saidflameexcluding layer.

2. A cartridge consisting of a casing which is open-ended and crimped atone extremity and is closed at the opposite extremity, a propellantcharge therein, a primer and means between said primer and saidpropellant charge for urging said charge against the crimped end of saidcasing.

33. A cartridge comprising a tubular casing having at one extremity anend wall having an orifice, an ignition cap mounted in said orifice,said casing being open at the opposite extremity and provided with anabutment, a propellant charge in said casing and a spring mounted insaid casing adjacent said end wall for urging said charge against saidabutment.

4. A starting device for apparatus intended to be put into motionquickly comprising the combination of a combustion chamber having avolume so restricted that the combustion in about 0.2 to 0.3 second ofthree pellets of smokeless powder each having a diameter of about 0.672to 0.675 inch and a total length of about 1.9 to 2.2 inch will producethereingas at a pressure in the range of about 15,000 to 25,000pounds'per square inch,.an open-work grate at one end of said chamber,means for urging a powder pellet against said grate, and independentmeans for igniting said pellet located at the opposite end of saidchamber.

5. The combination of a combustion chamber, a grate at one end of thechamber, a pellet of propellant material in said chamber, one end ofwhich is held in contact with saidgrate by a spring interposed betweenthe other end of said pellet and the opposite end of said chamber andmeans for igniting said pellet, said igniting means being located atsaid opposite end of said chamber. 5

EDWIN H. HULL. ARTHUR F. WINSLOW.

REFERENCES CITED The following references are of record in the 10 fileof this patent:

UNITED STATES PATENTS Number Number Germany Aug. 5, 1930

